1. Field of the Invention
This invention pertains to solid material comminution or disintegration in which rotating impeller type means provide an air stream for moving the web in paths through a shredder and out an outlet duct.
More particularly, such invention is directed to a method of an apparatus for shredding a web of material of indeterminate length, such as a bead of polymeric film, as it is moved in a direction transverse to movable and stationary shredding means by an air stream.
2. Description of the Prior Art
Apparatus for and methods of shredding a web of material, such as polymeric film, are known to the art.
U.S. Pat. No. 3,545,686 to Brown is typical of such known apparatus for shredding sheets of polymeric materials. In the Brown apparatus, a movable cutting blade having a sawtooth cutting edge and a stationary cutting blade having a sawtooth cutting edge interdigitate upon moving the movable cutting blade for piercing and tearing the polymeric film advanced across and parallel to the stationary cutting blade.
Another apparatus for shredding sheet material, in which the sheet is moved between bed knife teeth and a fly knife, as the sheet is fed or advanced in a direction transverse to the bed knife and fly knife teeth is shown in U.S. Pat. No. 2,635,693 to Gibby. The fly knife is one of a set of such knives uniformly spaced around the face of a rotating disc. The plastic sheet is fed by a pair of nip rollers over the upper face of the bed knife so as to be cut by the fly knives as they descend. The rolls are driven by a suitable drive to advance the sheet a predetermined distance after each fly knife passes and before the next descends. The patent primarily involves the intermeshing bed knife and fly knife, which are adapted to maintain a minimum of clearance upon wearing, machining or sharpening.
One of these problems has been the tendency of the film or the tough, flexible bead trim to wrap the rotor shaft or rotating blades carrying the shredding means. This is particularly true in the case of thin or light gauge films. In many instances, the wrapping of the rotor shaft or blades by the bead or film creates a jerk or pull on the bead causing it to break or the film to tear, and thereby directly cause major interruptions in the film making operation. Further, such apparatus often require very close knife settings or clearances to cause complete shearing, or shredding, of these films, which may have a thickness of as little as 0.00006 of an inch and, of course, bearing tolerances and temperature differentials limit the practical use of apparatus with such close clearance requirements. These clearances also may cause the bead to break or tear due to jerks or pulls on the bead. And, lastly, the tough, flexible nature of the film or bead of polymeric material, particularly oriented polyethylene terephthalate film, along with its thinness, make it an extremely difficult material to handle and shred. All of these problems are solved by the method and apparatus for shredding a web of material, that comprise the instant invention.